Indoor/outdoor thermometer systems for measuring an outdoor temperature and conveniently displaying the outdoor temperature on an indoor display are known in the art. Conventionally, these systems utilize a wired transmission medium between the indoor and outdoor components. These conventional systems suffer the disadvantage of requiring a wire with a temperature sensing device to penetrate an opening in a window or outside wall to measure the outside temperature. The inconvenience of having to create and close off such an opening limits the practicality of such a thermometer.
To alleviate some of the problems and drawbacks of wired thermometer systems, wireless indoor/outdoor thermometer systems employing radio frequency waves have been developed. U.S. Pat. No. 4,608,565 to Sakamoto discloses an indoor/outdoor thermometer including a temperature transmitting unit and receiving unit disposed on opposite sides of an exterior wall or window. The problem with this system, however, is that the transmitting and receiving units must be mounted on opposite sides of any one of a wall, petition or window so as to be located substantially adjacent to one another. Thus, in order to locate an indoor display at any convenient location, extra wiring would have to be run from the receiving unit to the desired location of the display. Moreover, the use of radio frequency transmission is not consistent with low power consumption and hence, is not conducive to the use of a long lasting and low cost battery such as a lithium type battery. Thus, a homeowner cannot avoid the inconvenience and cost of frequent battery replacement.
Other prior art systems are disclosed wherein sensed temperature data is transmitted optically to a remote receiver. U.S. Pat. No. 4,848,923, issued to Ziegler et al., teaches a measurement system which converts sensed parameter signals into light pulses which are transmitted to remote evaluation units. The Ziegler system employs a quartz measuring transducer coupled to an oscillator wherein the resulting frequency of oscillation is representative of the value of the sensed parameter. One problem with this system is that the data transmission method is not conducive to a free space medium because ambient noise will severely degrade the performance. To operate this system in a noisy environment such as a home or office would then require the use of a fiber optic transmission medium. Therefore, Ziegler does not teach a simple wireless system that can be adapted for practical use in an indoor/outdoor thermometer application. Moreover, Ziegler does not teach a low power consumption system compatible with a long lasting low cost battery such as a lithium type cell.
Thus, there is a need for an indoor/outdoor thermometer system employing a physically small outdoor unit mounted to, or in proximity to, an outer window surface to transmit outdoor temperature data to an indoor display unit mounted on any conveniently chosen indoor room location. There is also a need for such a thermometer to be of low power consumption design for long lasting maintenance free operation. There is a need for such a thermometer to provide accurate and reliable temperature measurements in a noisy environment with temperature data updated every few minutes.
The present invention, which utilizes an infrared data transmission link to transmit coded temperature data, provides such a thermometer system.